Ozymandias was so fixated on his status that he failed to find a balance between emotion and ambition, hence why "the hand that mocked them and the heart that fed" as the heart is usually seen as the seat of love yet here it doesn't love and provides nothing, but instead takes/"feeds" on whatever it needs. Alternatively the heart represents emotion whereas the hand is mechanical. This idea of balance/lack of balance may link to how Ozymandias abused his power and was uncontrollable.